Walking around the mounds, Professor Paul Butler says the Mounds are world famous – for stumping geologists.

"We’ve figured out plate tectonics. We’ve figured out the extinction of the dinosaurs, but nobody can come up with a convincing theory about the origins of these mounds that everybody’s pretty much happy with,” Butler says.

Hypotheses abound

The most credible one has to do with glacial melting patterns, that left the dirt mounds here during the ice age. It's often referred to as "the sun cup theory" – referring to shapes created by melting glaciers. The leading research on it has support from the US Geological Survey. Scientists there are using LIDAR imaging technology (bouncing lasers off of the earth's crust) to get data to support their theory.

Very popular over the years, perhaps because it's cute and kind of funny, is the theory that native gophers created the mounds.

Some scientists say they caused Mima's unique profile as they inhabited the prairie and built their nests. These researchers point out that gophers can move up to five tons of earth per year. And that there are lots of piles of stones between the mounds that look like what the prolific pocket gophers tend to leave around. But there's no actual evidence to prove this theory.

In fact, there's nothing inside the mounds themselves but dark brownish black soil, which is part of what gives them their unique profile. Unlike more common mounds, however, the composition of the ones at Mima Prairie lack the striping that geologists refer to as normal soil "horizons."

Other scientists say ancient earthquakes made the Mima Mounds … or floods.

Extraterrestrials?

There are even wacky theories about the Mima Mounds and three-eyed aliens from outer space.

That last theory doesn’t fly with most folks – and especially not with Dale Rutledge, a 91-year-old farmer, who lives next to the mounds in what might be the oldest house in Thurston County.

”I think it’s a bunch of hogwash,” Rutledge says.

Farming legacy nearby

Rutledge says his father was a school teacher and the first postmaster in Little Rock, where the Rutledge house is located. The little rock the town is named for is in their front yard; it was used by women riding side saddle, who needed help mounting heir horses after getting their mail.

“It was hard to count the cattle over there because they could be in the other side of a mound and you couldn’t see ‘em – some of them were that high. Some of them were pretty steep alright,” Rutledge says.

The tallest of the Mima Mounds are over eight feet.

Rutledge says he remembers seeing this for the first time when he was about three years old.

“It was kind of barren looking. But it was beautiful, really," Rutledge says.

A little-known landmark

A small part of the land is protected as a National Natural Landmark. It received this status in 1966, from the National Park Service, for its representation of our nation's natural landscape. The site is one of only 17 such landmarks found in Washington state.

Birdie Davenport, with the state department of Natural Resources, helps care for it.

She says she got hooked on Mima Mounds one night nearly 20 years ago, while putting out some fires that they had lit to burn off invasive species and encourage native wildflowers.

“And the moon was out and this fog had settled down around the mounds and so it was just incredibly beautiful, with the fog surrounding every mound. ... So, it was like a little hemisphere, floating above the fog with the moonlight, shining on the fog,” Davenport says, adding that she still likes to ride her horse through the landscape nearby.

An enduring puzzle

Geologists like Professor Duncan Foley, who teaches first-year students at Pacific Lutheran University, continue to enjoy wondering about it what caused the Mima Mounds.

“There’s a lot yet to learn. That’s part of the fun, ” Foley says.

Others agree that what caused them doesn’t matter so much; when you come to a special spot, you know it.

“Whether it’s Mount Rainier, or on the water, or whatever. Mima Mounds has its own kind of aesthetic beauty," Davenport says.

So the next time you’re driving along I-5 near Olympia, think about taking some time to explore this iconic puzzle yourself.

Who knows, you might just see it before the mystery of its origins is solved.

About the Series

What sorts of things in the Pacific Northwest have you wondered about? Attributes you find endearing, odd, even irritating.